Wireless cellular communication networks can comprise a plurality of mobile user equipment (UE) devices and a number of base stations (BS). A base station is generally a fixed station, and may also be called a base transceiver system (BTS), an access point (AP), a node base (NodeB), or some other equivalent terminology. As improvements of networks are made, the NodeB functionality evolves, so a NodeB is sometimes also referred to as an enhanced, or evolved, NodeB (eNB). In general, NodeB hardware, when deployed, is fixed and stationary, while the UE hardware is portable.
The mobile UE can comprise portable hardware. The mobile UE, also referred to as a terminal or a mobile station, may be fixed or mobile device and may be a wireless device, a cellular phone, a personal digital assistant (PDA), a wireless modem card, and so on. The phrase “Uplink communication” (UL) can be used to refer to a communication from the mobile UE to the NodeB. The phrase “downlink communication” (DL) can be used to refer to communication from the NodeB to the mobile UE. Each base station contains at least one radio frequency transmitter and at least one receiver used to communicate directly with mobile UEs. Similarly, each mobile UE contains at least one radio frequency transmitter and at least one receiver used to communicate directly with the NodeB. In some cellular networks, the mobiles cannot communicate directly with each other but have to communicate with the NodeB.
A reference signal (RS) is a pre-defined signal known to both transmitter and receiver. The RS is typically transmitted in order for the receiver to estimate the signal propagation medium. This process is also known as “channel estimation.” Thus, an RS can be transmitted to facilitate channel estimation. Upon deriving channel estimates they are used for demodulation of transmitted information. This type of RS is sometimes referred to as De-Modulation RS or DM RS. The RS can also be transmitted for other purposes, such as channel sounding (SRS), synchronization, channel state information (CSI) measurement, channel quality information (CQI) measurement, or any other purposes. The Reference Signal (RS) can be sometimes called the pilot signal, training signal, or any other equivalent term.
As the number of antenna continues to increase in wireless technology, the complexity in transmitting RS signals has increased. There needs to be improved systems and methods to transmit RS signals.